Many different types of sheet handling apparatus are known for performing a range of different operations on sheet-like material. Especially, many paper-handling devices are known, such as printers, photocopiers and folder/inserter machines. In these devices, a plurality of sheets are stored, often in a stack, until such time as the sheets are required for a sheet-handling operation. The sheets are then fed one-at-a-time into the sheet handling apparatus from the stack, and passed to an appropriate machine location where the sheet handling operation is performed.
In a simple sheet feeder, sheets are fed from the top or bottom of a stack of sheets by a pre-feed roller. The pre-feed roller engages the top or bottom sheet and feeds it towards the sheet handling apparatus. Typically, the feeding operation causes a shingling effect, whereby pre-feeding the top sheet simultaneously causes several further sheets to be fed due to frictional contact between the adjacent sheets. This shingling effect creates an overlapping system of sheets being fed into the sheet handling apparatus. In order to ensure that sheets are fed one-at-a-time to the sheet handling apparatus, the sheet feeder is further provided with a separator system. Such systems typically comprise a separator roller, which continues to feed the sheets received from the pre-feed system, and a separator pad or stone located opposite the separator rollers for retarding any further sheets, thereby allowing only a single sheet to pass under the feeding action of the separator roller.
However, such a simplistic sheet feeder is not always appropriate. For example, when a plurality of envelopes or folded or stapled sheets is stacked in a vertical stack (i.e. when each sheet-like element is substantially in a horizontal plane with adjacent sheet members located above and below it) then the sheet-like material does not form an ordered stack. This can lead to a stack of sheet-like material which is curled either in the corners or around the edges due to the extra thickness of folded, stapled or seam portions. This can present problems since when such a curled stack becomes large it is impossible for a typical sheet feeder to correctly engage the sheets in the stack in order to feed them into the sheet handling apparatus. Due to the uneven manner in which contact is made with the top sheets in the stack, the sheet being fed may become twisted or skewed as it is fed into the sheet handling apparatus, leading to damaged sheet material or a machine jam.
In prior art devices, bulky or awkward materials are traditionally stacked in a manner designed to reduce the forces acting on the sheet elements. Typically, sheet material such as envelopes are formed into a near-horizontal stack (i.e. with each envelope lying substantially in a vertical plane with adjacent envelopes located in front of and behind it). The front envelope in the stack is then engaged by feed rollers which rotate to feed the envelope down and forwards into a horizontal configuration before feeding the envelopes into the sheet handling apparatus. Such an arrangement reduces compressive forces between the envelopes, hence reducing shingling or envelope damage, but is costly in terms of the size of the stacking tray required to hold a sufficient plurality of envelopes, or is otherwise limited by the envelope stacking system having only a small capacity.
Alternatively, top-feeder devices may be used for envelopes, but these encounter limitations. Top feeders have the problem that material is presented to the feed element in a non-uniform manner, as thin material stacks (above 100 envelopes) can present extremely curled profiles at the top of the stack (the material which will be fed first). This is especially apparent with envelopes, considered to be the worst-case material to feed, as there are so many different types, each with different weights and constructions. As such, existing top feeders remove this element of variability by limiting the stack height, allowing only low capacities (typically only 100 pieces as a maximum). Even then, the performance of these feeders is still questionable.
Such envelope feeders are mainly, although not exclusively, used on folder/inserter machines for automatically feeding sheet material, in various forms, into envelopes which are held open ready to receive the desired contents. Typically, such a folder/inserter has means for storing a plurality of sheets forming the pages of a mail document. These pages are fed into the folder/inserter machine where they are folded automatically and then inserted into a waiting envelope. The envelopes are held in an envelope feeder section of the machine from which they are transported to an insertion location to await receipt of the folded mail package. The envelope and contents are then fed through an envelope sealing section of the machine before being ejected into a receive tray or bin.
Traditionally, the use of such folder/inserter machines has been dominated by large organizations, for instance banks, utilities companies and Governments, who require a means for producing a large number of mailpieces addressed to specific individuals and each containing unique printed material therein, potentially private to the recipient. Machines employed for these purposes are typically extremely large, and operate at a very high throughput, i.e. they produce mailshots potentially comprising hundreds of thousands of individually-addressed mailpieces in a short amount of time. Organizations having a national or international audience might need to produce hundreds of thousands of such mailpieces in a single day.
However, folder/inserter machines are rapidly becoming more widely accepted amongst medium and small-sized businesses. Such businesses still require the capacity to produce a large amount of outgoing mail, but to a smaller audience. Further, such businesses are incapable of affording the associated costs of running and operating a highly complex mailing apparatus of the type used by large organizations. Instead, folder/inserter machines of reduced complexity, and of a size suitable for SOHO (small office/home office) operation have been developed. Such machines are typically capable of producing mailshots comprising from a few hundred to one or two thousand mailpieces. These machines must be able to readily accept paper in the size and format typically used within an office environment, and similarly must be able to store and fill envelopes of the types most commonly used in the SOHO environment. Therefore, a folder/inserter for the SOHO environment will typically have an envelope feeding mechanism capable of storing several hundred envelopes in a stack. These envelopes are subsequently fed to a feeder/separator which separates a single envelope from the stack and feeds it to a waiting position where the envelope is held open and the desired printed material is inserted thereinto, as described above.
A balance has, therefore, existed in prior art machines between the necessity, on the one hand, to provide a sufficient quantity of envelopes without constantly stopping operation to replenish the supply, and the desire, on the other hand, to provide the envelopes one-at-a-time at a high rate-of-feed without unduly increasing the size of the envelope feeder to accommodate increased storage (in particular the size of the feeder “footprint” which effectively determines the actual space occupied).